Autumn Equinox

According to the calendar, and the weatherman, today is the autumnal equinox.  From what I undestand, and equinox is when there is exactly the same amount of daylight hours as nighttime hours.  And yet the weatherman claims that the day where the equal amount of hours will occur is actually going to be a few days from now.  So that makes me wonder why the “powers that be” have proclaimed today to be the equinox!  Do you have an explanation?  I sure don’t!